The present invention relates to bioactive glass compositions. More particularly, the present invention relates to improved compositions of bioactive glass including particles having size ranges significantly lower than previous compositions. The present invention also relates to a method of treating tooth hypersensitivity.
Tooth hypersensitivity is a common problem which affects about 40 million adults in the United States, 10 million of which can be considered chronically affected. Kanapka, Dent. Clin. North Am., 34:54 (1990). It is estimated that some 17% of adults in the U.S. have at least one or more sensitive teeth. Hypersensitive teeth may be sensitive to cold, heat, air or sugary foods.
The incidence of tooth hypersensitivity increases with age. Tooth hypersensitivity is believed to be related to the general increase in exposed root surfaces of teeth as a result of periodontal disease, tooth brush abrasion, or cyclic loading fatigue of the thin enamel near the dento-enamel junction. When root surfaces are exposed, dentinal tubules are also exposed. Dentinal tubules are naturally present in the dentinal layer of the tooth and they provide for an osmotic flow between the inner pulp region of the tooth and the outer root surfaces.
The currently accepted theory for tooth hypersensitivity is the hydrodynamic theory. Greenchill and Pashley, Journal of Dental Research, Vol. 60, pp. 686-698 (1981). This theory is based on the belief that open exposed dentinal tubules allow fluid flow through the tubules. This flow excites the nerve endings in the dental pulp. Clinical replicas of sensitive teeth viewed in a scanning electron microscope (SEM) reveal varying numbers of open or partially occluded dentinal tubules. (See FIGS. 1 and 2).
Certain dental procedures may result in a weak smear layer of dentinal debris 2-5 microns in thickness that covers the tooth surface and masks the tubules. in vitro, this smear layer is a normally occurring artifact of sectioning or preparing the tooth structure. A smear layer is easily removed by brushing or by other acids naturally present in the mouth or foods. When a smear layer is present, the fluid flow that can occur through the dentin is only a few percent of that possible following acid removal of the smear layer, which opens and enlarges the tubules. Accordingly, it is necessary to remove any smear layer when experimenting with the efficacy of a tooth hypersensitivity treatment in order to simulate sensitive dentin.
There is a growing body of evidence that occlusion of the dentinal tubules of a sensitive tooth by resin infiltration, varnish coat, or crystallite precipitation results in reduction or elimination of the hypersensitivity. The duration of relief, however, is highly variable. Hypersensitivity usually reappears because of tooth brush abrasion, presence of acid challenges in the mouth, or degradation of the coating material.
For example, a two-step procedure involving application of a calcium nitrate solution and a potassium phosphate solution to the tooth has been found to produce numerous calcium phosphate crystals. Kaminske et al, J. Dent., Res., 69:68 (1990).
Increasing concentrations of oxalic acid in the food bolus derived from dietary sources up to 1.14 g/l have also been found to yield precipitation of a deposit at the tooth surface. A maximal response was found to be obtained at a level of 0.1% (w/v) oxalic acid equivalents. Greater levels of oxalic acid did not yield greater protection of teeth. It has been postulated that the deposited material is calcium oxalate, resulting from interaction of the oxalic acid with calcium in the saliva. Gortner et al, J. Nutr., 32:121 (1946). The level of calcium in saliva is very low, however, thus the treatment is not very successful.
Alkali metal or ammonium oxalate have also been used to reduce tooth hypersensitivity. The low pH of the solution is believed to mobilize calcium and phosphate from the hard tissues (U.S. Pat. No. 4,057,621).
In addition, a 3.0% (w/v) monohydrogen monopotassium oxalate solution has been found to occlude dentinal tubules. Pashley et al, Arch. Oral. Biol., 23:1127 (1978). However, the treatment regimen deposits very few crystals on the dentin surface or within the tubules, and these deposited crystals are readily removed by water irrigation. Knight et al., J. Periodontal, 64:366-373 (1993).
Desensitizing dentifrices with potassium oxalate have been found to provide temporary tubule occlusion. Pashley et al., J. Periodont., 55:522(1984). Potassium oxalate is thought to react with the smear layer to increase its resistance to acid attack as well as reduce its permeability. It is thought that the crystals produced when dentin is treated with potassium oxalate are calcium oxalate. Pashley et al, Arch. Oral Biol., 30.731 (1985).
A two-component kit including a first 1.0-30% (w/v) neutral oxalate solution, such as dipotassium oxalate, and a second subsequent 0.5-3.0% (w/v) acidic oxalate solution, such as monopotassium-monohydrogen oxalate is described in U.S. Pat. No. 4,538,990. It is claimed that the neutral oxalate forms large crystals over the dentinal surface, and the acidic oxalate forms smaller crystals around and about the previously formed larger crystals to form a combined uniform layer of microscopic crystals.
Studies on the occlusion of dentinal tubules by deposition of crystals from potassium oxalate-based media (30% w/v K2C2O4) have shown variable results, purportedly due to variations in the size and number of crystals generated by the two solutions. These variations in size and numbers of crystals may depend on such factors as the pH of the solutions. The rate of crystal formation is influenced by the local Ca2+ ion concentration and the acidic 3.0% (w/v) solution of KHC2O4 generates an extremely high local calcium ion concentration by etching the tooth. As a result of the extremely high local calcium ion concentration, there is greatly accelerated formation of abundant crystals to yield the desired reduction in hypersensitivity. Muzzin et al, J. Periodont., 60:151 (1989). However, the source of ionized calcium within the dentinal fluid is not explained and the extremely high local calcium ion concentration is not defined.
A widely used one-step method for occluding dentinal tubules, PROTECT(trademark) (J. O. Butler, Chicago, Ill.), involves the application of a solution of KHC2O4 to the tooth surface. This solution does not contain calcium salts because it is believed that etching of tooth structure by the reagent contributes a more than adequate supply of Ca2+ to enable sufficient precipitation and crystal formation when the compound is applied to the tooth surface or in the tubule.
All of the above referenced materials use biologically inactive inorganic or organic components that will occlude the open tubules for a limited time period. Normal habits including the eating of acidic foods and vigorous toothbrushing will remove the materials from the tubules allowing fluid flow and a recurrence of sensitivity. In addition, literature has demonstrated that simple rinsing with water significantly reduces the number of tubules occluded with many of the available anti-hypersensitivity agents. Knight et al, Journal of Periodentology, Vol. 64, pp. 366-373 (1993).
Bioactive and biocompatible glasses have been developed as bone replacement materials. Studies have shown that these glasses will induce or aid osteogenesis in a physiologic systems. Hench et al, J. Biomed. Mater. Res. 5:117-141 (1971). The bond developed between the bone and the glass has been demonstrated to be extremely strong and stable. Piotrowski et al., J. Biomed. Mater. Res. 9:47-61 (1975). Toxicology evaluation of the glasses has shown no toxic effects in bone or soft tissue in numerous in vitro and in vivo models. Wilson et al., J. Biomed. Mater. Res. 805-817 (1981). However, the glass has been reported to be bacteriostatic of bacteriocidal most likely related to the change in pH induced by the dissolution of the ions from the surface of the glass and lack of bacterial adherence to the glass surface. Stoor et al., Bioceramics Vol. 8 p. 253-258 Wilson et al (1995).
The bonding of the glass to bone begins with the exposure of the glass to aqueous solutions. Na+ in the glass exchanges with H+ from the body fluids causing the pH to increase. Ca and P migrate from the glass forming a Caxe2x80x94P rich surface layer. Underlying this Caxe2x80x94P rich is a layer which becomes increasingly silica rich due to the loss of Na, Ca and P ions (U.S. Pat. No. 4,851,046).
The behavior of the bioactive glass as solid implants in a dental application was reported by Stanley et al., Journal of Prostetic Dentistry, Vol. 58, pp. 607-613 (1987). Replicate tooth forms were fabricated and implanted into extracted incisor sockets of adult baboons. Successful attachment of the implants to surrounding bone was seen after histologic examination at six months. Clinical application of this technique is presently available for human use. Endosseous Ridge Maintenance Implant ERM(copyright). Particulate bioactive glass has been used for periodontal osseous defect repair (US Pat. No. 4,851,046) utilizing a size range of 90-710 xcexcm and a compositional range described in the following chart.
Previously described data has shown that 60% silica is beyond the limit of bioactive melt derived glasses. Okasuki et al. Nippon Seramikbusu Kyokai Gakijutsu Konbuski, Vol. 99, pp. 1-6 (1991). The use of bioactive glasses for bonding to dentin has not been previously described. Moreover, these bioactive glasses are not suitable for treating tooth hypersensitivity.
Previously, bioactive glasses have been used only in larger size ranges and have only been applied to bone. The 90-710 xcexcm size range was determined to be the most effective for periodontal applications when in direct contact with bone. However, size ranges smaller than 90 xcexcm were ineffective due to their high rate of reactivity and rapid resorption at the bony site. Moreover, size ranges smaller than 90 xcexcm were determined to be ineffective in soft tissue sites also due to the presumption that the smaller particles were removed by macrophages (see U.S. Pat. No. 4,851,046). A size range of less than 200 xcexcm was also found to be ineffective in certain bone defects (see U.S. Pat. No. 5,204,106) due to the high rate of reactivity.
U.S. Pat. No. 4,239,113 (xe2x80x9cthe ""113 patentxe2x80x9d) also describes the use of a bone cement. The ""113 patent only discloses bioactive glass ceramic powder having a particle size of 10-200 microns. Moreover, the ""113 patent also requires the use of methylmethacrylate (co)polymers and vitreous mineral fibers.
Tooth dentin is very different from bone. The organic component of dentin (approximately 40%) makes most systems that will bond to bone and tooth enamel ineffective. Most current materials used for treatment of desensitization rely on materials that have been optimized for the bonding to bone and tooth enamel by their interaction with the inorganic components. As a result, even the most effective treatments are short lived. Therefore, there is a need in the dental field for a material that would chemically react with the surface of dentin and intimately bond to tooth structure, which would significantly reduce the reopening of dentin tubules due to contact with oral fluids.
It is therefore one object of the present invention to provide a composition that will accomplish at least the partial occlusion of dentinal tubules by chemical and physical interaction with the tooth structure.
It is a further object of the invention to provide a method of using a bioactive glass composition to reduce tooth hypersensitivity.
The present invention relates to a bioactive glass composition including particulate bioactive and biocompatible glass having the following composition by weight percentages:
and a particle size range less than 90 xcexcm, wherein the particulate bioactive and biocompatible glass includes an effective dentin tubule occluding amount of particles less than about 10 xcexcm. The present invention also relates to a method of treating hypersensitive teeth and a method for occluding dentinal tubules.